This invention relates to an organic electroluminescent display (hereafter xe2x80x9corganic EL displayxe2x80x9d) in which the organic light-emission element is protected from water vapor and similar and provided with an extended lifetime, and a method of manufacture of an organic EL display.
In recent years, organic EL displays have attracted attention as flat panel displays. Organic EL displays can be driven by a DC voltage, so that the driving circuitry can be simplified, and there is no viewing-angle dependence like that of liquid crystal displays; and they have the further feature of high brightness by virtue of self-emissive operation. And, they have the further feature of a quite fast response time compared with liquid crystal displays.
Conventional organic EL displays are explained referring to FIG. 1. FIG. 1 is a cross-sectional view of a conventional organic EL display. An organic EL element 2, formed by layering of a cathode 2a with a photo-emissive layer 2b formed from a plurality of organic substances 2b1, 2b2, 2b3 and an anode 2c, is provided on the glass substrate 1. For simplicity of narrative, references for the above-mentioned layers of the organic EL element are omitted from the following description, and, hence, the organic EL element 2 is only referenced as a whole. The organic EL element 2 is easily affected by water vapor, and the lifetime is shortened when there is a large amount of water vapor present; hence the organic EL element 2 must be shielded from water vapor. To this end, a metal cap 3 is provided which seals the organic EL element 2 and shields the element 2 from water vapor. The metal cap 3 is bonded with adhesive 4 to the glass substrate 1. A desiccating agent 5 which absorbs water vapor is provided on the surface inside the metal cap 3 opposing the organic EL element 2.
Next, a method of manufacture of a conventional organic EL display configured in this way is explained. First, an organic EL element 2 is formed by layering an anode, organic film and cathode, not shown, by evaporation deposition onto large-size (for example, 300 mmxc3x97400 mm) transparent-electrode glass as the glass substrate 1 in a nitrogen environment, so as to prevent the intrusion of water vapor. At this time, a plurality of organic EL elements 2 are formed in regular fashion on the transparent-electrode glass. Next, a metal cap 3 is formed from a metal (for example, SUS steel or Al), and BaO is bonded to the interior as a desiccating agent 5. Each of the organic EL elements 2 provided on the transparent-electrode glass is covered by such a metal cap 3, which is bonded to the transparent-electrode glass with adhesive 4. Finally, the transparent-electrode glass is divided into separate organic EL elements 2. In this division, a scriber or similar may be used. By this means, organic EL displays are manufactured.
In a conventional organic EL display, one metal cap 3 is provided for each of the plurality of organic EL elements provided on the transparent-electrode glass, entailing difficulties and impeding improvement of productivity. Further, due to the high temperature of the surrounding environment, organic EL displays may be affected by heat. Also, heat generated during optical emission may have consequences. That is, because the materials of the glass substrate 1 and of the metal cap 3 are different, thermal expansion coefficients will differ. Hence heat induces thermal expansion of different magnitudes in the glass substrate 1 and in the metal cap 3, so that stress occurs in bonding portions. As a result, water vapor may penetrate into the metal cap 3 from the bonded portion using the adhesive 4, giving rise to the problem of a shortened lifetime for the organic EL display. Moreover, because the metal cap 3 is not translucent, light emitted by the organic EL element is absorbed, further promoting increases in temperature of the organic EL display.
The present invention was devised in light of these circumstances, and has as an object the provision of an organic EL display, and a method of manufacture of an organic EL display, enabling improved durability and improved productivity.
In order to achieve the above object, the organic EL display of this invention is an organic EL display comprising a first translucent substrate; an organic EL element, provided on the first translucent substrate, and formed by layering of an anode, a photoemissive layer formed from a plurality of organic substances, and a cathode; and a second translucent substrate which seals the organic EL element; and characterized in that the second translucent substrate comprises a depression at the location opposing the organic EL element.
Thus in order to seal the organic EL element, the second translucent substrate, of the same material as the first translucent substrate on which the organic EL element is provided, is used. As a result, the thermal expansion coefficients of the first translucent substrate and the second translucent substrate are the same, so that even if the first translucent substrate and second translucent substrate expand due to heat in the neighboring environment or to heat generated during light emission, they expand in the same way. Consequently no stress occurs at the bonding portion, and the degree of sealing of the organic EL element can always be maintained at a high level. As a result, intrusion of water vapor can be prevented, so that the durability of the organic EL display can be improved.
Further, a second translucent substrate is used as the means of sealing the organic EL element, so that light emitted by the organic EL element is transmitted from the second translucent substrate. Because of this, it is possible to avoid heat generation due to absorption of light emitted from the organic EL element by the sealing means, as for example in cases where the organic EL element is sealed using a substance which is not translucent, such as a conventional metal cap Consequently increases in the temperature of the organic EL display caused by light emission can be prevented.
Further, a plurality of organic EL elements can be formed on the first translucent substrate, depressions formed in the second translucent substrate at sites corresponding to each organic EL element by, for example, chemical etching or mechanical etching, the first and second translucent substrates bonded such that organic EL elements and depressions oppose each other, and the bonded first and second translucent substrates divided into individual organic EL elements.
Consequently numerous organic EL displays can be manufactured at once, and productivity can be improved.